RF switches are a key building block in wireless systems and find many uses in applications such as mobile phones and wireless LANs. The act of switching radio frequency signals in an integrated circuit is carried out by an RF switch circuit. Many technologies exist for the design of integrated RF switch circuits.
An RF switch may comprise multiple switching elements which control the flow of RF power between different points in the particular application. Switching elements are comprised of transistors that are stacked. The number of transistors in a stack is determined by the maximum RF voltage that can be developed across the complete stack and the maximum voltage that can be tolerated across an individual transistor without introducing limitations to either reliability or linearity performance of a device. RF integrated circuits (ICs) are subject to stringent linearity specifications which require tight limits on the level of distortion that a device can introduce on an RF signal. Linearity requirements may be expressed by specifying different parameters such as harmonics generation, intermodulation distortion (IMD2, IMD3) or intercept points, (IP2, IP3). Irrespective of how requirements are specified the linearity performance is determined by distortion introduced on the RF signal by RF transistor stacks. Adoption of 4G/LTE standards places ever increasing demands on linearity requirements of components such as RF switches. The RF transistor stack is becoming a limitation in achieving the required linearity performance on SOI CMOS process that must be overcome.
There is therefore a need to provide an RF transistor stack which addresses at least some of the drawbacks of the prior art.